// namespace Components {

  export class Header {
    constructor () {
      const elem = document.createElement("div");
      elem.innerHTML = "this is header2";
      document.body.appendChild(elem);
    }
  }

  export class Content {
    constructor () {
      const elem = document.createElement("div");
      elem.innerHTML = "this is content2";
      document.body.appendChild(elem);
    }
  }

  export class Footer {
    constructor () {
      const elem = document.createElement("div");
      elem.innerHTML = "this is footer2";
      document.body.appendChild(elem);
    }
  }

  // 子命名空间 --  嵌套命名空间namespace
  // export namespace SubComponents {
  //   export class Text {}
  // }

// }
